Communication is often desirable between linked modules which are subject to rotation relative to each other. For example, communication may be desired through a linkage that includes a ball-joint or a gimbal, or communication may be desired between two modules that thread together, whereby the process of threading one module into the other during assembly could lead to twisting, kinking, and possibly breaking of conventional wires. In particular, it is sometimes desirable for a plurality of data transmitting sources, such as sensing and monitoring circuits, to communicate with a receiving destination, such as to a system control module. In various circumstances, the plurality of data transmitting sources may not share a common power supply or ground with each other and/or with the data receiving destination, such that electrical interconnection therebetween could be problematic.
One approach to enabling such communication is to provide lengths of wire or fiber optics which are preconfigured to withstand the mechanical motion required. For example, if two sections are be joined by threading them together, then the connecting wires can be pre-wound in the opposing direction, so that they are unwound as the two sections are joined. However, these approaches are subject to wires or fiber optics being kinked, tangled, and or stretched as the sections are joined.
Another approach to providing such communication is to use mechanically slidable connections such as slip rings, but these are subject to wear and are generally unreliable. And if the data transmitting sources do not share a common ground or power supply with each other and/or with the data receiving destination, direct electrical connection can lead to ground-loops and to other forms of electrical noise and interference.
Another approach is to transmit signals over a wireless radio link such as a wireless network. However, for many applications this approach is too complex, too expensive, and too unreliable, and can also be prone to electronic interference from outside sources.
Yet another approach is to use an optical data link, whereby optical signals, for example from one or more light-emitting diodes, are transmitted by data transmitting sources in one of the modules and are detected by an optical detector cooperative with the data receiving destination located in the other module. It will be understood that the use of the term “optical” herein is not limited to visible light, but is used herein to refer to all frequencies of light, including light in the visible, infra-red, and near ultra-violet bands. However, maintaining alignment between the sources and the detector can be difficult. One approach is to position the light source and detector along a mutual rotation axis shared by the two modules. However, this is not always convenient, and is problematic when there is a plurality of data transmitting sources.
U.S. Pat. No. 4,753,506 to Einhorn teaches a-solution wherein a plurality of off-axis LED's fixed to one module transmit signals to a single off-axis detector fixed to the other module, whereby the LED's and detector are arranged such that light from at least one of the LED's will always be detected by the detector regardless of the relative angular orientation between the modules. However, the approach of Einhorn is not easily extended to cases where it is necessary for a plurality of sources to communicate with a single receiver.
What is needed, therefore, is a data communication interface which provides electrically isolated signal communication between a plurality of transmitting sources cooperative with a transmitting module to a common signal receiving destination cooperative with a receiving module, the transmitting module and the receiving module being subject to rotations relative to each other about a shared axis.